Our work focuses on IGF-I regulation of gene expression for P-450 cholesterol side-chain cleavage (P450scc), the rate-limiting enzyme in the steroidogenic pathway. We identified an IGF-I response element (IGFRE) of the porcine P450scc gene that binds Sp1(stimulator) and polypyrimidine tract-binding protein (PTB)-associated splicing factor (PSF, repressor). In this proposal we will investigate mechanisms of PSF regulation of IGFRE activity. Studies will be conducted in a stable porcine granulosa cell line, the JC-410 cells. We hypothesize that PSF repression of the IGFRE involves a mechanism that prevents IGF-I-stimulated phosphorylation of Sp1. In specific aim 1 we will determine IGF-I-mediated Sp1 phosphorylation sites having already demonstrated that IGF-I stimulates phosphorylation of threonine 739 on Sp1, a known erk 1/2 phosphorylation site. In specific aim 2 we will investigate the erk 1/2 signaling pathway as at least a partial mechanism for regulating IGF-I stimulation of the IGFRE through Sp1 phosphorylation. Finally, we will investigate protein kinase C (PKC) iota as a modulator of PSF-Sp1 interactions regulating the IGFRE (specific aim 3). We will determine the fundamental mechanisms whereby IGF-I controls P450scc gene expression through interactions of Sp1, PSF, and PKC iota. This knowledge will increase our understanding and provide the basic background for novel concepts on hormonal control of ovarian steroidogenesis.